Backyard Chickens and Lawn Care Products

[osprey28]

I have a small flock consisting of 2 Rhode Island Reds and 5 Red Stars, all hens. I want to be careful about what type of lawn care products are being used on my property as the birds are permitted free range and graze. Can anyone recommend an organic pre-emergent crab grass preventer and lawn fertilizer that won't harm/contaminate the birds or their eggs?

Thanks.

 

[chickflick]

I haven't a clue, but maybe someone else knows.....